First thing to use is going inside a 
                    Compo
                    Composite 2D Layer, Shape layer and 3D Layer together. [Ctrl] + [Shift] + [N] to create a new composition after opening Smode
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                     advanced parameters.
		  Inside quality part of the composition parameters, uncheck "automatic", then you got here the multi-sampling and pixel Type parameters.
                      - Multi-sampling can help you improve quality of a composition containing 3D object. Effective until a value of 8, going above is a waste of performances. You can complete this effect with the 
                     Anti Aliasing
                    FXAA post effect
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Anti Aliasing
                    FXAA post effect
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                    .
                      - Pixel Type will help you changing pixel depth (8/16/32 bits). This will be very useful to have more precise gradients but especially to have a nicer displacement from a displacement map with a 
                     Displace
                    Move each pixel in a direction given a distortion map
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Displace
                    Move each pixel in a direction given a distortion map
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                    .
                    
 
                    
                    
                      If your displacement map is only an image (and so you don't have access to theses parameters) another way to transform a 8bit image into a 16bit one is just to add a 
                     Legacy Blur
                    Blur the image
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Legacy Blur
                    Blur the image
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                     and turn it's pixel type to 16bits (or higher):
                    
 
                    
                    
                      In terms of particles. If you see theses ugly artifacts due to bad alpha pre-multiplying:
                    
 
                    
                    
                      ...then just go inside of the sprite points renderers and either uncheck the depth buffer test and write (faster) or activate the depth sorting of the particles (slower but beautiful)